Automatic telephone-exchange system



June 24, 1930. E. H. CLARK ET AL I AUTOMATIC TELEPHQNE EXCHANGE SYSTEM Filed Sept. 29, 1928 9 Sheets-Sheet '1 m m Em 2Q 2Q 3 3Q 3% N3 9 m 506A h. CLARK .WVENTURS' MRRE W CARPEN ER (26. Know June 24, 1930. E. H; CLARK AL AUTOMATIC TELEPHONE EXCHANGESYSTBI Filed Sept. 29, 1928 9 Sh eets-$heet 2 [DEAR h! CLARK I WVENTDRZ YMRREN WEARPEA/m? A TTURIVEY June 24, 1930. E. H. CLARK AL 6 AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Sept. 29, 1928 9 Sheets-Sheet 3 H NR 1 m 4 MW Sq as m .p HQMV E Emu/- I 1 wmq -ww fin \QNN. J L ML aw Q. w v 0R; mwm c "U \Q 4 QM fifi Ml? Q R M .wnn RN. .HHHH'HHHHH A w xnnw nw www \R Sn l u June 24, 1930. E. H. CLARK AL AUTOMATIC TELEPHONE EXCHANGE SYSTEI Filed Sept. 29, 1926' 9 sheds-sheet 4 EDGAR/7! 62AM "W MRREN W CARPENTER ATTORNEY June 24, 1930. CLARK ET AL 1,767,962

' AUTOMATIC TELEPHONE EXCHANGE sfis'TuI 9 Sheets-Sheet 5 Filed Sept 29, 1928 [DEAR hf GLMW' W Vtwmfis' 1444mm W GAflPENTE/i HYQ4 ATTORNEY June 24, 1930. E. H. CLARK 'tAL.

AUTOMATIC TELEPHONE EXCHANdE SYSTEI Filed Sept. 29, 1928 9 Sheets-Sheet 6 $3 g I [DEA/'7 H CLARK #vvavrms. M REL-N W CARE/V753 Arrbnlvfr June 24, l930. E. H. CLARK ET AL AUTOMATIC TELEPHONE EXCHANGE SYSTBI Filed Sept. 29, 1928 9 Sheets-Sheet 7 R 0% W QNN @x \R R M a M Sm R R Em m. P .m we Q ao w a w 6 H W V MGR, M J as W V n. R 1U F Dn 7 u A Q 1 v W M Q \Q\ I! Wm bu R I N mm S m \Q NQ QR L, J A UH A J .u FIR W T i T f \w\ mmn wwm v Q n ma FFQQQ gE M M .M M M QR NR qliil 5 wk 3 wvm h Mn m w A I wwm aw QR Q R @k RN .Q\ l NQQ v A v v 1 v R bum 1% \w\ \w\ June 24, 1930, E. H. CLARK AL- AUTOMATIC TELEPHONE EXCHANGE SYSTEI Filed Sept. 29, 1928 9-'Sheets-Sheet 8 EEG June 24, 1930. E. H. CLARK ET AL AUTOMATIC TELEPHONE EXCHANGE SYSTII Filed Sept. 29, 1928 9 Sheets-Sheet 9 [DEAR h BLAH/r WVENI MRREN WUARPLNTER B) AT TDRNfI' Patented June 24, 1930 "res EDGAR H. "CLARK, OF FOREST HILLS, AND WARREN W. GARE-ENTER, "OF QUEENS VILLAGE, 'YOIRK, ASSIGNOR'S TO BEL'L TELEPHGNE LABORATOitIES, OF NEW 'YORK, 4N. TL, 4A CORPORATION OF N-EXV YORK AUTOMATIC TELEPHONE-EXCHANGE SYSTEM Application filed September 29, 1928. Serial .No. 309,1?2'7.

This invention relates to telephone ex change systems and particularly to those systerns 'n lrerein mechanical switching apparatus is employed in the establishment of connections between subscribers lines terminating in manual oflices of the exchange area. and subscribers lines terminating in machine switching offices of the'same area.

The invention has for its object the -simplification of apparatus necessary for the establishment of such connections and the increased economy in the first cost and maintenance thereof.

In exchange areas which are being changed through theinsta'llation o'f-maehine switching apparatus to operate on a full mechanical basis rather than on a strictly manual basis, it is desirable that provision be made for-the extension of calls originating in a manual oiiice of the exchange to any of the outlying automatic oiiices through the control of the selector switches in the called automatic oifice by mechanism located at the calling inanuahofiice. As the exchange area becomes more nearly ifull mechanical :through the changing of a greater number of the :manual o'fiices to automatic offices, the need for such controlequipment for the remaining manual oiiices becomes more essential.

By this plan the operator who has answered the callisenahled .to establish the interoifice connection which leads to adist-ant automaticoliice without assistance, the entire operation of the switches at the distant automatic oiiice being governed by mechanism at the originating sitions, divided into two main groups,.all positions having access to a plurality of groups of outgoing trunks, one group leading to each of the automatic :ofi'ices of the exchange area. Each position is further equipped with a sender controlling key board, a set of ofiice keys, and oiiice code register relays, and a register switch of the step-by-step type which has two functions, first, to control the setting of trunk selecting switches to select a ,group of trunks to a desired oiiice, corresponding to the oiiice code registered at the position, and second, to register the number of an idle trunk in the desired ofiice group selected by the trunk selecting switches for the purpose ofoperating indicating lamps at the position to indicate the number of the particular selected trunk.

The senders are divided into two groups, corresponding to the grouping of the operators positions, and an idle sender in a group is taken for use by a position through a'sender selecting switch individual to the position.

In order that selected senders may become associated with idle trunks, out goingto desired automatic oifices, groups of link circuits are provided. Each of these links terminates at one end in a pair of sender hunting switches, each hunting switch having access to one of the groups of senders, and at the other end in a selector switch which has access to a group of trunks outgoing to particular automatic oilices. Since links in each group of links are alloted for use in extending connections to particular automatic oiiices, the senders are provided with link selecting switches which may be directed to select a link which has access through its associated trunk selector to the oiiice desired.

In the operation of the system the operator who answers an outgoing callat-the originating manual oilice first depresses an of-- lice key at her postion corresponding to the oiiice in whichthe desired line terminates and thereby causes the sender-finder switch associated with her position to hunt for an idle sender iii the group of senders serving the position, and causes'the registration of the otfice code of thedesired line on the office code registers of her position. She may then depress figure.

keys in her key board to register on the numerical registers of the sender the numerical designation of the desired line. As soon as the sender becomes associated with the operators position, a control circuit is established from the register switch of the position to the link selecting switch of the sender and these switches operate in unison until the position register assumes a posi tion directed by the operated tens code register relay of the position.

The selected link then hunts for the trunk selector and a control circuit is established thereover from the trunk selector through the sender to the position register and the selector and register then operate in unison until the register assumes a position directed by the operated units code relay of the posi tion. In this manner a group of trunks outgoing to' the ofiice in which the desired line terminates is selected. The position register is then restored and is reoperated in unison with further hunting movements of the selected selector until such selector has selected an idle trunk from a sub-group of trunks in the selected group to the desired office. In its reoperated position the register causes trunk number indicating lamps at the position to be lighted to indicate to the operator the number of the selected outgoing trunk. The operator then plugs into the jack of the indicated trunkand her position apparatus is freed for another call. The sender then proceeds to operate the selector switches in the selected automatic office in accordance with the numerical designation registered on the registers thereof in the well known manner.

Referring to the drawings, Figs. 1 to 9 inclusive, arranged in accordance with the diagram of Fig. 10, disclose so much of a telephone system embodying the principles of this invention as is necessary to a comprehensive understanding thereof.

Fig. 1 shows one of a plurality of answering operators positions of a manual office provided with cord circuits for extending subscribers lines over interofiice trunks outgoing to distant dial switching offices. One of these outgoing trunks terminating in a dial switching ofiice is illustrated in this 'Fig. 2 shows a set of numerical keys, one ofiice key, a portion of the office code registers, a sender-selecting switch, and control relays of the operators position shown in Fig.1.

Fig. 3 shows a trunk number indicating equipment individual to the operators position of Fig. 1 for indicating to the operator the number of the interoffice trunk over which a connection to the desired dial switching ofiice is to be extended. 0

Figs. 4, 5, 6 and 7 taken together show one of a plurality. of register senders available for the use of operators positions of one manual oflice. Fig. 4 shows two steering switches and certain control relays of the sender. Fig. 5 shows additional control relays. Fig. 6 shows relay registers for registering the numerical digits of wanted line numbers and Fig. 7 shows counting relays for setting the switches of the dial switching ofiice under the control of the registers of Fig. 6 and a link selector switch for se lecting a link of a group over which access to the desired dial switching office may be had. 7

Fig. 8 shows a link having sender finder switches for hunting for the sender in either of two groups of senders which an operator has taken for use for extending a connection from the sender toward the group of trunks extending to the desired dial switching oflice.

Fig. 9 shows a selector individual to the link of Fig. 8 for further extending a' con ncction to a desired trunk group.

Fig. 10 is a diagram showing how the various figures should be arranged with relation to each other.

General description 0 f apparatus The selector switches 123 and 124, diagrammatically illustrated in Fig. 1 and located in the distant dial switching ofiice 122,-

'F. J. Scudder 1,895,977, granted November The steering switches 400 and 450 of Fig. 4, the sender selector 250 of Fig. 2, the link selector 750 of Fig. 7 and the sender finders 800 and 850 of Fig. 8 are of the rotary single motion step-by-step type driven by stepping magnets from terminal set'to terminal set and are so arranged that the brushes move forward to the next set of terminals upon the deenergization of the corresponding stepping magnet. Of these switches the sender selector 250 and the sender finders 800 and 850 have no normal position, these switches remaining in the position to which they were last moved upon the release of their associated circuits. 7

The selector switch 950 of Fig. 9 and the position switch 350 of Fig. 3 are of the step by-step type having both a vertical and a rotary motion. Each switch is provided with.

a pair of brush sets and corresponding'banks i 'nation.

trated, and two groups oi office code relays,

only one relay of each group having been disclosed. As many OillCQ keys are provided at each position as there are dial switching offices in the exchange area to which the manual oiiice has access. Each such group of code register relays comprises eight relays, only the first of each group having been disclosed. The register relays of one group registers the tens code letter of an oflice designation and the relays of the other group re ister the units codeletter. By suitable interconnection with the ofii'ce keys it is possible by the depression or a single key to register the first two letters of an oiiice des-' For example, as will be hereinafter more fully described the depression of key 200 registers the or fice code CA for the ofiice CAnal on the tens register relay 202 and on the units register relay 201.

The operators positions of the manual oilice are divided into two groups and the senders are likewise divided into two groups. Any operatofs'position of one group may through the sender selectors individual to such positions, such asselector 250, have access to .any sender of one group of senders and similarly the positions of the other group have access to the senders oi the other group. For connecting a selected sender with groups oftrunks outgoing to the o'liices to which the manual office has access, a plurality of groups of link circuits are provided, each group of link circuits having access to a certain plurality of such oi'hces. Each sender is provided with a link selecting switch 750, which is set in accordance with the first code letter of the oiiice designation which the operator registers at her position through the depression or an oiiice key, to select idle links from the group over which access to the desired oiiice may be had. The selection or such a group of links closes a start circuit for starting all idle links of such group to hunt for the calling sender, the first link to find such sender seizing it and the others being dismissed. Two sender finders are provided for each link to connect with the calling sender, regardless of which sender group such sender is located in. A selector such as 950 is permanently paired with each link and responds to the second code letter of the ohice designation which the operator registers at her position to complete the selection of the desired group of trunks and to then select an idle trunk from such group. The trunk hunting movements of such selector 950 are registered by the position switch 850 to cause the operation of indicating lamps to indicate to the operator the number o1 the trunk so selected.

Detailed description It is believed that the invention will be best understood from a detailed explanation of the manner in which a connection may be established. To this end it will be assumed that the subscriber or line 100 in the manual oliice wishes to converse with the subscriber of line 125 in a distant dial switching oflice 122. Upon removing his receiver from the switch-, hook the calling subsc iber completes a circuit for the energization of line relay 104, which in turn causes the illumination oflamp 105. The operator upon observing the illumination of lamp 105 answers by inserting plug 102 of one of her cord circuits into the jack 101. The insertionof the plug in the jack completes a circuit from battery through the lamp 107, resistance 106, sleeves of plug 102 and jack 101, winding of relay 108 to ground. Relay 103 operates and severe the circuit of relay 104:, which causes the line lamp 105 to become extinguished. The receiver being ofi' the switchhook the. insertion of the plug in the jack also completes a circuit from battery through the lower left winding of repeating coil 109, the winding of relay 110, rings of plug 102 and jack 101, over the loop of the line returning over the tips of jack 101 and plug 102, upper left winding of repeating coil 109 to ground. Relay 110 operates in this circuit and closes a circuit from battery through its contact, resistances 108 and 106, thence over the path previously traced through the winding of relay 103 to ground. This latter circuit shunts the lamp 107, causing the same to remain extinguished. The operator next depresses the listening key 112 connecting her headset into conversational relation with the calling line and ascert'ains the wishes of the calling subscriber.

Upon learning that he wishes to talk with a subscriber at a distant oflice 122 theoperator depresses the otlice key 200 of Fig.2, which key corresponds to such distant oiiice. For

the purposes of this description it will be assumed that the wanted line number is CAnal 3981 and that therefore upon the depression of key 200 the No. 2 units code register relay 201 is operated over a circuit extending from battery through the right winding of relay 201, the left contacts of key 200 to ground through the right winding of relay 206 and the tens code register relay 202 is operated ver a circuit from battery through the wind ing of relay 20 1-, the left back contact of relay 203, the right winding of relay 202, the right contacts of key 200, the right back contact oi relay 203, the left winding of relay 220 to ground at the inner right back contact of relay 207. Relays 201, 202, 204:, 206 and 220 energize in these circuits, relay 220 looking over its right winding and inner right contact over the back contact of release relay 205,

conductor 229 to ground at the left back contact of release magnet 300 of position switch 350. Relays 201 and 202 close a mutual locking circuit for each other extending from battery through the left winding and left contact of relay 201, the left winding and left contact of relay 202, conductor 231, to ground at the outer left contact of relay 220. Relay 206 also looks over its left winding and left contact to ground on conductor 231.

Relay 204 which is operated in the operat ing circuit of relay 202 locks through the winding of relay 203, right front contact of relay 204 to ground on conductor 231 and closes a circuit for lamp 232, extending from battery through said lamp, the left contact of relay 204, conductor 233 to ground at the outer right contact of relay 301. Relay 203, however, does not operate in the locking circuit of relay 204 until the key 200 is released, since both terminals of its winding are connected to ground. Lamp 232 which lights upon the energization of relay 204 remains lighteduntil the trunk number is completely registered on the position switch 350. Upon the release of key 200 relay 203 energizes, opening at its back contacts the initial energizing circuits of relays 201, 202, 204 and 220 and all other register relays of the position to prevent interference with the call should the operator depress another oflice key before the call has been completed and her position equipment released. The code register relays 201 and 202 also prepare circuits for controlling the positioning of switch 350 will be hereinafter described.

Relay 220 upon energizing also establishes a circuitfor relay 208. v extending from battery through the winding of relay 208. the inner left contact of relay 220 to ground at the right back contact of relay 207 and a circuit for lamp 209 extending from battery through lamp 209, the right back contact of relay 210, outer left contact of relay 220 to ground at the inner rightback contact of relay 207. Lamp 209 burns steadily at this time and relay 208 upon energizing connects the contacts of keyset 211 to battery through the winding of relay 210. Should the operator prematurely depress a key of the keyset, i. e. while the lamp 209 is burning steadily denoting that a sender has not yet been associated with her position equipment, relay 210 will operate, locking over its left contact to ground on conductor 231 and at its right contacts trans fers the lamp 209 from steady ground to in termittent ground through the interrupter 221. The lamp will thereupon flicker as a signal that the operator should release her position and start to call again. She may do so by depressing the release key 222, thereby operating release relay 205, which in turn releases relay 220 and all other operated relays of her position. Relay 208 upon operating also disconnects the key contacts of keyset 211 from conductors 223, 224 and 225, extending tobrushcs of the sender selector 250.

Association of an idle sender with the operators position Relay 220 upon operating also establishes a circuit for relay 227, extending from battery through the right winding thereof, the left back contact of relay 207 to ground on conductor 231. If the sender to which the switch 250 has access over the set of terminals upon which its brushes are at the time standing is busy, brush 214 will be connected to ground potential and relay 227 will thus lock over its left winding and left front contact and will establish 'a circuit for relay 207, extending from battery through the right winding of relay 207 to ground at the right contact of relay 227. Relay 207 upon energizing locks over its left winding and inner left contact to ground at the right back contact of release relay 205, connects ground to holding conductor 231 over its outer left front contact, at its inner right back contact disconnects ground from the operating circuit of relay 208 and lamp 209 and at its outer right front cont-act establishes a circuit extending from battery through the winding and contacts of magnet 234, the outer right contact of relay 207 to ground at the right front contact of relay 227 for advancing the brushes of switch 250 into engagement with the set of .terminals connected to the next sender. The removal of ground from the circuits of relay 208 and lamp 209 does not release saidrelay or extinguish said lamp as they still receive operating ground from the right front contact of relay 227. At its outer left back contact relay 207 opens the initial energizing circuit of relay 227. The switch 250 will continue to step until its test brush 2'14 fails to find busy ground potential when relay 227 will release, no longer having a locking circuit over its left winding. Relay 227 upon releasing opens the circuit of magnet'234 to arrest the further advance of switch 250, releases relay 208 to connect the keyset 211 to the brushes 243, 244 and 245 of switch 250, preparatory to enabling the operator to set the numerical registers of the selected sender, and extinguishes lamp 209 as a signal that arsender has been found. It will be assumed that the switch 250 has advanced to position its brushes upon the third set of terminals of its arcs. A busy potential is now applied to the test terminal 228 from ground at the inner right front contact of relay 207 over the left back contact of relay 227 and brush 214 for marking the sender busy to sender selectors of other positions, this ground potential being extended over conductor 242 in parallel through the windings of relay 406 and 600 to battery on conductor 408.

Relay 406 upon energizing prepares several Cir circuits At its outer left contact it places ground on conductor 409 for supplying locking ground to relays of the sender, at its outer right front contact it establishes a circuit extending from ground over conductor 402, brush 403 and the normal terminal of steering switch, 450, the outer left back contact of re lay 405, conductor 503 to battery through the right winding of relay 500 and at its inner left contact establishes a circuit for relay 404 extending from battery through the winding of relay 404, the inner left contact of relay 400, the outer left back contact of relay 407, the back contact of relay 427, conductor 455,

, the outer left back contact of relay 510, cenductor 504 to ground over the normal terminal and brush 420 of steering switch 450. At its inner right contact relay 406 locks from battery on conductor 408 over its winding and inner right contact, conductor 604 to ground and the inner lower front contact of relay 600. Relay 600 upon energizing connects ground over its upper front contact to con d-uctor 601 for furnishing locking ground for theregister relays of Fig; 6 and connects ground to conductor 618 for a purpose to be later explained.

Relay 404 upon energizing establishes a circuit for relay 705, which may be traced from abatter through the windine of relay 705. v 2' i) 1 conductor 401, the right back contact of relay 410 to ground at the right contact of relay 404.- Relay 705 upon energizing closes two circuits, one extendingfrom battery to the wil'iding of magnet- 412 over conductor 413, the outer left contact of relay 705, to ground at the back contact of counting relay 702, pr"- paring the magnet 412 for advancing steering switch 450 into position 2 and the other circuit extending from battery through the winding of relay 501, conductor 505, the inner left contact of relay 705, conductor 703, the right back contact of relay 510,. the left back contact of relay 514, the right back contact of relay 509 to ground on conductor 409'.

Operation link finder 750 in accordance with first code letter of office designation Relay 501 upon energizing establishes a circuit for relay 704, extending over the back contact. of stepping magnet 707, conductor 7 08,.the right back contact of relay 507, the left back contact of relay 508, the winding of stepping relay 502, the left contact of relay '501, the outer right front contact of relay contact a: circuit for stepping magnet 707 of the switch 750, which lattermagnet energizes, in turn: opening the circuit of relays 704 and 502;. Thus, as the switch 750 advances it causes the intermittent operation of pulsing relay 502. Upon the first energization of re lay 502 a: circuit is established for relay 407, extending. from battery through the winding of relay 407, the first position terminal and brush 4- 16 of steering switch 450, conductor 411 to ground at the front contact of relay 502. Relay 407 in turn opens at its outer left back contact the operating circuit of relay 404-, but'relay 404 being slow to release re- 111011151013912D0GC1 so long as-relay 407 receives impulses fromr'the steppin relay 502. At its inner left contact relay 40.1 establishes a circuit extending from ground over conductor 757, brush 247, conductor 226 the inner left back Contact of relay 301, winding of slowto-release relay 300, the right back contact of release magnet 300, the outer right back contact of rel'ay 305-to battery through the'winding of verticalmagnet some position switch 350. lvlagnet 304 energizes, advancing the position switch 350 one step vertically and relay 306 I energizes, supplying operating ground to the pulsing circuit previously traced to the windings of relay 502 and relay 704 in place of ground over the oft-normal contacts 330, which open upon the first vertical step of position switch 350.

Hi il n'iagnet 304'fully energizes relay 407 l 'ned'energized to hold the circuit ofmagnet 304 closed in a circuit extending froinbatterythrough the winding of relay 407, the left contact of relay 404, the right front contact of relay 407, conductor 230, thence as traced to ground over the back contact of magnet 304 and the front Contact of relay 306, even though the initial operating'ci nit of relay 407 is opened at the contact of relay 2. This is to insure that the magnet 304 will be energized until it has advanced the switch 350 a full step. As soon as magnet 304 completely energizes the pulsing circuit previously traced through windings of relays 502' and 7 04 is opened, and the holding circuit of, relay 407 is opened. Relay 407 thereupon deenerg-izes, opening the circuit of magnet 304' and relay 306. Magnet 304 then decner circuit for relays 502 and 704 and the above described operations are repeated for advancing' the switch 750 and the position switch 350 another step. Relay 306 being slow to release, does not deenergize so long as impulses are transmit-ted through its winding to operate magnet 304.

It has been: assumed that the first code letter registered upon the tens code register relay'202'i a s-C, having a numerical equivalent of 2. Therefore, when the position switch 350'has advanced. two steps vertically and the commutator brush 313 has been raised to the second segment of commutator 314, a circuit res, again establishing the pulsing will be closed from ground at the intermediate right contact of relay 220, the right contact of register relay 202, conductor 236, brush 313, thence over the inner right back contact of relay 301, conductor 235, and as previously traced to battery through the winding of relay 407. 'Relay 407 is thus prevented from deenergizing when the vertical magnet 304 completes its second energization .412. Magnet 412 then advances the steering switch 450 into position 2. With relay 501 released, the pulsing circuit through relays 704 and 502 is opened at the left contact of relay 501.

As soon as the steering switch leaves normal the previously traced circuit of relay 500 is opened and since at this time slow releasing relay 306 has not had time to deenergize, a circuit is established for relay 405 extending from battery through the winding of relay 405, the left back contact of relay 410, conductor 511, outer right back contact of relay 500, conductor 512, right back contact of relay 407, conductor 230, brush 246, conductor 235, inner right back contact of relay 301, conductor 302, back contacts of rotary magnet 303 and vertical magnet 304, outer left back contact of relay 301 to ground at the front contact of relay 306. Relay 405, upon energizing, looks over its inner right front contact to conductor 511 independently of the contacts of relay 410 and closes an obvious circuit for relay 410 which then operates and locks over itsinner left contact, conductor 513, the inner right back contact of relay 500 to ground on conductor 409.

With steering switch 450 in position 2 a energizing, establishes a circuit extending from battery through the winding of relay 711, the second position terminal and brush 715 of link selector 750, which it will be re called was advanced into position 2 in response to the registering of the first code letter C of the office designation, conductor 720 to ground at the outer left contact of relay 515. Relay 711, upon energizing, locks over its right front contact to ground on conductor 409 and at its left contacts establishes a test condition on conductor 723 to mark the send-'. or as calling to all sender finder switches of Relay 515 also establishes a circuit for operating all start relays, such as 801 of idle links of the group of links selected by the link selector 750. This circuit may be traced from ground atthe inner left front contact of relay 515, over conductor 517, brush 714, conductor 724, thence in parallel through the windings of start relays, such as 801. The circuit for relay 801 of the link shown in Fig. 8 is completed from conductor 724 over the right back contact of relay 804, the outer right back cont-act of relay 803 to battery, through the Winding of relay 801. With relay 801 energized a circuit is established for relay 805 extending from battery through the winding of relay 805, the right normal contacts of relay 806, the left back contact of relay 807 to ground at the inner left contact of relay 801. Relay 805 energizes, connecting the winding of relay 806 over the left front contact of relay 805 to ground over the left back contact of relay 807 and the inner left contact of relay 801, hereby causing the energization of relay 806. Relay 806, upon energizing, now looks over its inner right contacts to its operating circuit independent of the left contacts of relay 805, at its right normal contacts opens the circuit of relay 805 thereby releasing such relay and at its inner left contacts closes a circuit through the two left windings of relay 807. Relay 807, however, does not energize at this time since it energizes only when its three windings receive current in the same direction. With relay 805 released and relay 806 energized, a circuit is now established from battery through the right winding of relay 808, the left back contact of relay 805. the outer right contact of relay 806 to ground at the right back contact of relay 807. Relay 808 energizes in this circuit, at its inner right contact closin an obvious circuit for reenergizing relay 805 and at its outer right contact establishing a circuit for the stepping magnet 810 of sender finder switch 800 extending from battery through the winding and contacts of magnet 810, the intermediate left front contact of relay 801, the right contact of relay 805, to ground atthe outer right contact of relay 808.

If the set of terminals upon which the switch 800 is at the time standing is connected to a non-calling sender, ground potential will be connected over the back contact of relay 711 of such sender, conductor 723, the terminal upon which brush 809 is resting, the outer right front contact of relay 801, the left front contact and left winding of relay 808 to battery and relay 808 will therefore remain energized after relay 805 energizes ire-7,962

and opens its initial energizing circuit. If

releases, opening the circuits of relay 805 and magnet 810. In a similar manner other idle sender finders of the same link group are simultaneously ope-rated through the operation of their start relays, such as 801, to hunt for the callingsende-r.

Should two finders simultaneously find the calling sender a circuit will be established from battery through the right winding of relay 507, the inner right contact of relay 515., conductor 725, brush 716, the left front contact of relay '711, conductor 723, brush 809 of switch 800, the outer right contact of relay 801, the left back, contact of relay 808, the two right windings :of relay 807 to ground at the inner left front contact of relay 806. A similar circuit from brush 809 of the sender finder of the second link which has also found the same sender will also beclosed to battery-through the right windings of a relay similar to relay 807.. In this case, relay 507 and the two relays 807 will not receive sufficient current to operate and therefore a circuit will be closed by each relay 807 for the corresponding relay=808 extending from ground at the right :back contact of relay 807, the outer right front contact of relay 806, the inner left back cont-act of relay 805 to battery thro-ugh the Winding of relay 808. Relays 808will again operate in turn operating relays 805 and closing the circuits of stepping magnets 810 of the two finders to further advance the finders. Relays 808 will again lock up so long as the finders test the terminals of non-calling senders. Since one finder will undoubtedly fall slightly behind the other in testing for the calling sender, therefore, when the brushes of one finder, such as 800, again reach the terminals of the calling sender, the other finder will not have reached them and therefore 65 its left back contact opens the locking circuit of relay 806, whereupon relay 806 releases. As soon as relay 807 closes its right front contact relay 507 energizes and locks over its left Windingand inner left contact to ground on conductor 409 and closes a circuit from ground at its outer left contact over the secend position terminal and brush 453 of steering switch450 to battery through the contacts and winding of magnet 412 for advancing steering switch 450 into position 3. With steering switch 450 in position 8 the circuit of relay 404 is again established extending from battery through the winding of relay 404, the inn-er left contact of relay 406, the outer left back contact of relay 407, the back *contactof relay 427,conductor 455, the outer' left back contact of relay 510, conductor 504 to ground at the third position terminal and brush 420 of steering switch 450. When steeringswiteh 450 leaves position 2 relay 515 releases removing battery from the circuit previously traced through the right winding of relay 807. Relay 515 also :at its left con-' tacts opens the initial operating circuits of relays 711 and 801.

With relay 807 energized and relay 806 deenergized, a circuit is now closed for the relay 811 extending from battery through the winding of relay 811, the inner right contact of relay 801, the left back contact of relay 806, the left front contact I of relay 807 to ground at the inner left contact of relay 801. Relay 811, upon energizing, looks over its inner right contact, brush 812 to ground on conductor 618, at its outer right contact closes an obvious circuit for relay 804 for opening the start circuits 724 and 724 extending from both groups of senders to the start relays 801 and 803, thereby releasing relay 801, and at its intermediate right contact extends conductor 728 over brush 809 to the right winding of relay 807 independent of the inner right contact of relay 801 which is now open. At its left cont-acts relay 811 also extends conductors 902, v

908 and 910 from selector 950, over brushes 813, 814 and 815 of finder 800 to conductors 802, 727 and 726 extending to the sender.

At this point it may be explained that had a sender of the other group of senders been v calling, a sender of such group being dia grammatically disclosed at 830, the start conductor 724 would have been grounded at such sender and a circuit closed for start relay 803 of the link extending from conductor 724 s over the left back contact of relay 804, the outer left back contact of start relay 801, to battery through the winding of relay 803.

Relay 803 functions in exactly the same manner as relay 801 except that it establishes a circuit for the stepping magnet 820 of the sender finder 850 upon the energization of relay 808, whereby the finder 850 hunts for a sender in the group in which sender 830 is located. Also relay 803 prepares a circuit for relay 816 to establish connections from the sender 830 to the selector 950 individual to the link.

A circuit is now closed from battery through the winding of relay 915, over conductor 918, brush 812, conductor 618 to ground, whereupon relay 915 energizes, supplying at its right front contact locking ground for relays of the selector 950 and at its back contact opening at one point the operating circuit of release magnet 917. A circuit is also closed from battery through the left winding of relay 900 over off-normal contact 901, conductor 902, inner left contact of relay 811, brush 813, conductor 802, winding of relay 700, conductor 701 to ground at the intermediate left contact of relay 406. Relay 900 energizes in this circuit, but being low wound relay 700 does not operate. Relay 900, upon energizing, locks over its left frontcontact to ground at the front contact of relay 915 and at its outer right front contact prepares an operating circuit for the vertical magnet 903 of selector 950.

At the position switch 450 following the completion of the positioning of link selector 750 and the positioning of switci 350, relay 306 releases, opening the circuit of relay 405 and closing a circuit from ground at its back contact over the off-normal contacts 315, now closed, through the right normal contacts and winding of relay 305 to battery. Relay 305 operates, opening its own energizing circuit and looking over its inner right contacts to ground at the left back Contact of release magnet 300. At its outer right contact relay 305 substitutes the rotary magnet 303 for the vertical magnet 304 in the circuit previously traced, extending to the sender. 7

At the sender upon the release of relay 405 a circuit is established for relay 456 extending from battery through the winding of relay 456, the right back contact of relay 405, the left front contact of relay 410, conductor 511, the right back contact of rela 500, conductor 512, the right back contact'or relay 407, thence as traced over the back contacts of magnets 303 and 304, over the outer left back contact of relay 301, left front contact of relay 305 to ground at the left back contact of relay 316. Belay 456 energizes in this circuit and establishes a circuit for relay 500 extending from battery through the left winding of relay 500, over conductor 518, the inner right contact of relay 456, the third position terminal and brush 403 of steering switch 450 to ground on conductor 402. Re-

lay 500 locks over its inner left contact and brush 403 to ground independent of the coir tacts of relay 456, 'Relay 500, upon energizing, now opens at its inner right back contact the locking circuit of relay 410, which relay now releases opening at its outer left front contact the circuit of relay 456 which also releases. Relay 410, upon releasing, also ontablishes a circuit for relay 705 extending from battery through the winding of relay 705, conductor 401, the right back contact of relay 410 to ground at the right contact of relay 404 and relay 705 in turn establishes the previously traced circuits for relay 501 and magnet 412. ltelay 501 and magnet 412 now energize, magnet 412 preparing the steering switch 450 for advancing into position 4 and relay 501 establishing a pulsing circuit between the sender and the selector 950.

Setting the selector .950 in'aooordcmoe with the second ofiz'oe code letter A pulsing circuit between the selector 950 and the sender may now be traced from battery through the winding of relay 904, back contacts of rotary magnet 905 and vertical magnet 903, the inner right back contact of relay 906, the intermediate right back contact of relay 907, conductor 908, the intermediate left contact of relay 811, brush 814, conductor 727, the outer right back contact of re lay 709, the back contact of counting'relay 710, conductor 7 34, the right front contact of relay 507, the left back contact of relay 508, winding of relay 502, the left contact of relay 501, the outer right front contact of relay 500, conductor 512, the right back contact of relay 407, conductor z30, brush 246, conductor 235, the inner right back contact'of relay 301, conductor 302, the back contacts of magnets 303 and 304, the outer left back contact of relay 301, the left contact of relay 305 to ground at the back contact of relay 316. Relays 904 and 502 energize in the circuit. Relay 502, upon energizing closes a circuit for itself over its right contact, the right back contact of relay 515 to ground at the outer 7 left back contact of relay 522 independently of ground at the back contact of relay 316 and at its left contact establishes a circuit for relay 407 extending from battery through the winding of relay 407, the third position terminal and brush 416 of steering switch 450, conductor 411 to ground at the left contact of relay 502.

Relay 407 at its inner left contact establishes a circuit for rotary magnet 303 of the position switch 350 extending from battery through the winding of magnet 303, the outerright front contact of relay 305, the right back contact of release magnet 300, the wind- 7 ceive impulses due to the advanceof selector 950v and to retransmitsuch impulses through thewinding of relay-407. With relay 407 energized a' holding circuit for relay 407 is closed from, battery through. its winding, the left contact of relay 404, theright front contact of the relay 407, conductor 2,30, brush 247, conductor 235, the inner right back contact of relay 301, theback contacts of magnets 303 and 304, the outer left. back contact of relay 3.01, the leftcontact of relay 305to ground at the left back contact of relay 316 and also, to ground at the front contact of re lay 306. Relay 407 therefore does not deenergize until the rotary magnet 303 has fully energized to advance the switch 350 one step.

At the selector 950, upon the energization of relay 904, a circuit is closed for the-vertical magnet 903 from battery through the winding of magnet 903, the outer right front contact of relay 900 to ground at the inner left front contact of relay 904. Relay 904 also closes an obvious circuit for relay 909 which disconnects the tip and ring brushes of the selector during its vertical selection move ment. Magnet 903 energizes and at its contacts opens the previously traced pulsing circuit through the winding of relay 904 and thewinding of relay 502. The selector switch is thus stepped vertically one step, opening at the off-normal terminal 901 the initial energizing circuit of relay 900. Upon the opening of the pulsing circuit and the deenergization of relay 502, the initial energizing circuit of relay 407 is opened and upon the completion of the first stepofmagnet 303, the holding circuit of relay 407 is opened, whereuponiit deenergizes opening the operating circuit of magnet 303 which also deenergizes. At the selector 95,0 upon the deenergization of vertical magnet 903 the pulsing circuit previouslytraced is again established and relays 502 and 904 again operate, both performing the same functions previously described, to cause the further advanceof the selector 950 and of the position switch 350 another step. p 7

It has been assumed that the second code letter registered upon the, units code register relay 201 was, A, having a numerical equivalent of 2. Therefore, when the position switch. 350 has advanced two steps in j a rotarydirectiona-ndthe brush 308 is resting on. the second terminal of the second level ofbank 317, only the first two and tenth levels of such bank being disclosed, a circuit will be closed from groundat the intermediate right contact of relay 220 over the right contact of relay 201-, conductor 2'37, brush 308, thence over theinner right back contact of relay 301,. conductor 235 and as previously traced to, battery through the right winding of relay 407. Relay 407. is thus prevented from, deenergizing when rotary magnet303' completesits second step for such a period that the circuit for relay 404 is held open long enough to release relay 404. Relay 404 on releasing opens the circuit of relay 407 which thereupon releases andopens the circuit of rotary magnet303 and slow-torelease relay 306 of the position switch 350. Relay 404 upon deenergizing also opens at its right contact the previously traced cir-f cuit for relay 705 which deenergizes in turn opening thecircuits of relay 501 and magnet 412. Magnet 412 thereupon advances the steering switch 450 into position 4. 7 As soon as 'relay407 deenergizes the circuit previously traced for relay 404 extending over the outer left back contact of relay 407 is closed and relay 404 energizes. When the steering switch 450 leaves position 3 the locking circuit for relay 500 is opened at brush 403 and relay 500releases closing at its outer right back contact the circuit previously traced for relay 405 extending to ground at the front contact of slow-to-release relay 306 of the position switch. 350. Relay 405 energizes, locks and establishes the circuit of relay 410 as previously described and relay 410 thereupon lo'cksover itsinner left front contact, conductor 513, the inner right back contact of relay 500 to ground on conductor 409. l/Vith steering switch 450 in position 4 a circuit is at this time prepared for relay 521extending from battery, through the winding of this relay, the, left back contact of relay 520, con,- ductor 530, the fourth position terminal of brush 418, of steering switch 450, conductor 717 to ground at the right back contact of relay 522. r p 1 When relay 306 releases following the com-.- pletion of the last rotary step of position switch 350, the locking circuit of relay 405 is opened at the front contact of relay 306 and a circuit is established from ground at the back contact of relay306, over ofinormal contacts. 315, brush 307 and the terminal of bank 318 uponwhich it is resting, all ter,- minals of such bankbeingstrapped together but only the-first, two and tenth levels of such bank being shown, to battery through the winding of relay 316. Relay 316 upon energizing establishes at its left front contact a circuit for releasemagnet 300 of the position switch extending from ground at the front contact, of relay 316, over conductor ing the circuit of magnet 300. Magnet 300at its left back contact also opens the locking circuit of relay 305 which releases, and disconnects ground from conductor 229, releasing relay 220; Belay 220, upon releasing, in turn removes ground from conductor 231 at still maintained on conductor 231 for holding operated relays of Fig. 2 energized over. the outer left contacts of relay 207.

l/Vithrelay 405 released'and relay 410 still energized a circuit is now established for relay 456 extending from batterythrough the winding of relay 456, the right back contact of relay 405, the left front contact of relay 410, conductor 511, the outer right back contact of relay 500, conductor 512, thence as previously traced to the outer left, back contact of relay 301, over off-normal contacts 330, nowclosed, since switch. 350 has been restored to normal, to ground at the left back contact of release magnet 300. Relay 456, upon energizing, now looks over its inner left contact, the right front contact of relay 410 to ground at the right contact of relay 404, and establishes a circuit for relay 407 extending from battery through the winding of relay 407, the left contact of relay 404, the outer left contact of relay 456, conductor'531, the left contact of relay 520, conductor'530, the fourth position terminal and brush 418 of steering switch 450, conductor 717 to ground at the right back contact of relay 522. a

Relay 407 upon energizing closes a circuit for the vertical magnet 304 of the position I switch 350 in series with relay 306 extending from'battery through the winding of magnet 304, the outer right back contact of relay 305, the right back contact of release magnet 300, the winding'of relay 306, the inner left back contact of relay 301, conductor 226, brush247, conductor 757 to ground at the inner left front contact of relay 407. Until the magnet 304 fully energizes relay 407 is locked through its winding, the left contact of relay 404, the right front contact of relay 407, conductor 230, brush 246, conductor 235, the inner right, back contact of relay 301, conductor 302, the back contacts of magnets 303 and 304, the outer left back contact of relay 301 to ground over the off-normal con tacts 330 and the left back contact of magnet 300, andafter relay 306 energizes to ground at its front contact. The energization of relay 407 also establishes a circuit for relay 1 500 extending from battery through the right winding of relay 500, conductor 503,

the left back contact of relay 405, the outer right front contact of relay 456 to ground at the inner left contact of relay 407. Re-

, lay 500 thereupon energizes opening at its inner right back contact the locking circuit of relay, 410, thereby releasing relay 410 whichin turn opens the holding circuit of relay 456'which also releases. Relay 500 also closes a-locking circuit at this time for relay 521 extending from battery through the winding and inner right front contact of relay 521, over theinner right front contact of relay 500 to ground on conductor 409 and establishes a locking circuit for itself extending from battery through 1ts rlght windlng over conductor 503, the left back contact of contact of relay 500, conductor 536, brush 1 403 and its fourth position terminal to ground on conductor 402. 7

Relay 456 upon releasing opens the initial energizing circuit of relay 407; If at this time the magnet 304 of the position switch has advanced such switch a full step, the

holding circuit of relay 407 is opened at the back contact of magnet 304 and relay 407 deenergizes'opening at its inner left contact the operating circuit of magnet 304 and relay 306. Magnet 304 deenergizes but'relay 306 being slow to release does not 'deenergize before its circuit is again closed as will be presently described. A circuit is now closed for relay 705 extending from battery through the winding of relay 7 05, conductor 401, the right back contact of relay 410 to ground at the right contact of relay 404. Relay 705, upon energizing, closing the pre viously traced circuits for relay 501 and mag net 412. Magnet 412 upon energizing pre pares to advance steering switch 450 into position 5.

Selection of idle tmmlc group by selector .950 and partzal registration of tens digit of trunk mtmber Y ting the position switch in accordance with the vertical stepping of the selector to register the tens group of trunks which the selector now proceeds to hunt for. It will be assumed that the group of trunks that is selected by the selector 950 extending to the distant office 122, comprises 40 trunksappearing in the second and third levels of the banks of suchselector'and as inresponse to the second code letter A, the switch shaft of selector950 has positioned its brush sets opposite the second level of each bank, commutator brush 911,

will now be standing on commutator segment 912 Should all of thetrunks of the second level of both banks be busy there will be no ground potential connected to the segment 912 and the circuit to be hereinafter traced from the brush 911 through the right wind mg of relay 900 will not be effective to differentially release relay 900,

As aconsequence, a circuit is completed from battery through the Winding ofrelay 904, thenceas previously traced to the winding of pulsing relay 502, the left contact of relay 501, theouter right front contact of relay 500, conductor 512, the right back con-' tact'of relay 407, conductor 230, brush 246, conductor 235, the mner. right back contact of relay 301, conductor 302, the back. contacts of magnets 303 and 304, the outer left back contact of relay 301 to ground at the front contact of relay 306, relay 306 not yet having had time to release since the position switch 350 took its previous Vertical step. Relays 502 and 904 are both energized, relay 502 locking to ground over its-right front contact, the right back contact of relay, 515 and the outer leftback Contact of relay 522, and closing at its left contact the previously traced circuit for relay 407. Relay 407 energizes and at its inner left contact closes the previously, traced circuit for vertical magnet 304 and relay 306 of the positionswitch 350, and locks over 'the le'ft contact of relay 404 and its own inner right front contact, thence to ground at the front contact of relay 306 over the circ'uit previously traced.

Magnet 304 upon energizing advances the position switch 350 another step to position its brushes opposite the second lGVGl'O-f their respective banks. Relay 306 which was pre viously energized when the switch 350 took its first step and did not have time to release, is maintained energized at this time. Relay 904 of selector 950energizes and again closes the previously traced circuit for the vertical magnet 903 which in turn opens the pulsing circuit through the'windings of relays 502 and 904 just traced, relay 904 in turn opening thecircuit of magnet 903. Thus, magnet 903 is operated and released to advancet-he switch shaft on step vertically to position the brushes opposite the third level of terminals in its banks. When relay 502 deenergizes upon the operation of vertical magnet 903 the initial energizing circuit of relay 407 is opened and when the vertical .magnet304of the position'switch completes its energization to advance the switch 350 a full step the looking circuit of relay 407 is opened and relay 407 releases, opening the operating circuit of magnet 304 and relay 306. .Magnet 304 thereupon releases.

It will be assumed that when the second selector has stepped to position its brush sets opposite the third level of its banks, the brush 911 encounters ground potential on the terminal 918 corresponding to the third bank levels of the selector. In Fig. 1 the terminal equipment of two trunks extending to the office 122 both appearing in jacks before the operator, has been illustrated, trunk 136, 137 being the first in the group of ten trunks appearing in the third level of the upper bank selector 950 and trunk 126, 127 being'the'tenth "of such group. In a similar manner ten other trunks extending to the office 122 appear in the terminals of the third level of the lower bank of the selector 950, but with their tip and ring conductors reversed. It will be noted thatsolong as any trunk inthe first group is idle ground will be connected to the commutator terminal 918 over the conductor 919 the outer back -contact of t'he cut-ofi relay of such trunk, for ex ample, relay 121,and over the outer back contact of the, sleeve relay of such trunk, for

example,relay 120. Similarly so long as any trunk of the other group often, one trunk of which is indicated at 920 is idle, gr.ound will be connected to the conductor 921, also connected to the commutator terminal 918. Thus brush 911 upon encountering ground potential establishes a circuit from such ground over brush 911 theright winding and inner right contact of relay 900, 'outer right back contactof relay 906, the outer right back contact of relay 907, conductor '910, outer left contact of relay 811,'brush 815, conductor 726, inner right back contact of relay 709, conductor 519, the left front contact of'relay 521, the inner left back contact of relay 510 to. battery through both windings. of relay 509. Relay 509 energizes and establishes a 1 circuit for-relay 514 from battery, winding of relay 514, front contact of relay 509 to ground at conductor 409. Relay 514 at its right contact shunt-s the left winding'of relay 509, thereby reducing the resistance of the circuit previously traced through the right winding of relay 900 sothat the right winding of this relay receives-sufficient current to cause the differential-release thereof. Relay 900 upon releasing opens the operating circuit of vertical magnet 903, to vprevent the further vertical stepping of the selector. Relay 509 upon energizing also opens at its back contact the energizing circuit of relay 501, whereby relay 501 deenergizes.

When relay 9 00 deenergizes the previously traced circuit through relay 509 is opened at the inner right front contact of relay 900 and relay 509 'dee'nergizes in turn opening the energizing circuit of relay '514. Relay 514 being slow to release momentarily closes a circuit for relay 510 before it releases, extending from battery through the winding of relay 510, the left front contact of relay 514, the right back contact of relay 509 to ground on conductor 409. Relay 510 upon energizing locks over its inner right contact, conductor 537, the fourth position terminal and brush 414 of steering switch 450, conductor 415 to ground at the inner leftloack contact of relay 522, at its inner left back contact opens the initial energizing circuit of relay 509' and at its outer left back contact opens the circuit of relay 404. Relay 404 thereupon releases opening the previously traced circuit for relay 705.

Relay 705 upon releasing now opens the circuit of magnet 412 advancing steering switch 450 into position 5. As soon as the steering switclrleaves position 4 the locking circuit of relay 500 is opened at brush 403 whereupon relay 500 releases, in turn releasing relay 521. Also, the locking circuit of relay 510 is opened, releasing relay 510. With relay 500 de'energiz'ed the circuit pre- 

